It goes back to what you had for available bombers and try to compare them to the American bombers of 1942/43. The American bombers had engines with turbos that would give 1000hp max continuous to 27,000ft or above and they weren't good enough to keep 4 engine bombers doing 200+mph at altitudes over 20,000ft in large formations. Mainly because by the time you get to max cruise lean you are down to around 750hp. The Melrin XX wasn't much different. Max lean cruise was around 725-760hp depending on altitude (and without the turbo that was down around 18-20,000ft). Problem for the Melrin XX is that as you go above 18-20,000ft the cruise power drops. The B-17 could hold 750hp cruise to 35,000ft. Makes cruising at 24-26,000ft a breeze.
Perils P40 Archive Data
The V-1650-1 is listed at econimical cruise of 2650 RPM 725 hp, low blower, auto-lean at 20,000 ft. (not too much less than the max cruise power at 2320 RPM ... but I suspect British and american standards for maximum cruise might differ a bit)
Also odd that the minimum specific consumption on the merlin is at high RPM, it's certainly not the case on the allison. (granted, minimum specific consumption and most economical power settings for a given aircraft are different matters, but still that's much different from the cruise figures for the V-1710) ... and reading the figures more closely shows 'maximum cruise' at 2,320 rpm high blower 18,000 ft having significantly more power and LOWER fuel consumption than at 2,650 20,000 ft ... so the labeling of those cruise power settings seem a bit odd.
The USAAF chart also leaves a big gap between 20k and 30k ft, but given 20k is still in low blower (while 30k is in high if only 580 hp) that still implies a bit of room for variables there. (though running at lower RPM in high supercharger gear seems to make the most sense in the 20,000 ft range too)
So the interim solution seems to be, use bombers that have lousier gun defense than the Americans used, bombers that can't fly any faster, bombers that can't fly as high, and bombers that can't (if you try for high altitudes) carry much more than the American bombers. And use escort fighters that had trouble matching the German fighters over the coastal areas without being burdened with long range fuel tanks. Why the panic over getting MK IX Spits in service? Because the MK Vs couldn't to the job and yet somehow adding several hundred pounds of tanks and fuel will improve the combat results?
How much does this comparison differ from the experiences with Luftwaffe precision day bombing during the BoB? (aside from them having no real heavy bombers, though several of the medium bombers were higher performing and/or better armmed)
Hmm, actually the He-111H series with 7 defensive guns during the BoB seems better covered than the british heavies, let alone the later H models with improved armaments. (given the relative sizes, more akin to the B-17's defensive arrangement ... or B-25's )
Lack of waist and ventral guns on british heavies leaves a lot of open spots. (wellington too)
I don't think higher than 20000ft is needed in 1941/42 in fact if only Allison engined escorts are available I was thinking as low as 15000ft for bombers since fighters could provide top cover at about 20000ft before being forced down to 15000ft where the bombers they were protecting were (Allison's full throttle height). At 15000ft bombers are more vulnerable to FLAK but the numbers of guns and numbers of radar was nowhere near as high as it would become and fighters are far more dangerous.
They would have been capable of some very accurate bombing over the highly industrialised Ruhr in the summer and fall of 1941.
If the Merlin XX is available for the escorts then Attack altitude over 20000ft would seem to be practical.
Mustang IIs (9.6 supercharged allisons) might have been good enough to provide top cover for bombers cruising at 20,000. Or ... better than overweight spitfire Vs (spit IXs with extended fuel capacity would be another matter). Speed was the big disadvantage of the Spitfire V next to the 190s, and the P-51A fared much better there even at 20,000 ft.
But ... historical Mustang IIs (and P-51As) came too late to be useful anyway and too few with the Mustang III coming online very soon after. (a hypothetical V-1650-1/Merlin XX powered mustang I alternative is another matter though)
But aside from that, long-range spitfire models with expanded fuel and streamlined armaments seem the most practical option. Merlin powered P-40s were too heavy and also a bit late into service anyway ... and arguably worse than the historical Mustang I/Ia even with the limited power at altitude.
It is common to quote losses in percentages. However losses are in aircraft which have to be replaced. I doubt that any group of 10 bombers (4 engined heavies) trying to raid deep into Germany at any time during the war in daylight would suffer less than 60% losses and would probably be 100% more often than not. You need a massive number of bombers and escorts to keep the losses down to 10%. The UK had just staggered through the BoB in 1940 , I think it is very very fanciful (as some have) to think about forces of 500 x 4 engined bombers and escorts in 1941 when we were struggling to cope with defence of the UK plus N Africa.
Wouldn't this be another argument in favor of focusing on shorter/medium range bombing objectives? (more like the RAF already was, just with the shift to daylight precision bombing)
The Mustang was an Accident, not clever planning, and forever linked to the idea of "P-40 replacement" for low to medium altitude utility fighter. The Wing Rack and Fuel drop tank ideas first originated with the notion of keeping the NAA Mustang line (and plant and workers) employed by slipping the A-36 procurement into available AAF Dive Bomber funding in early 1942. The notion of Merlin engine modification originated with RR in the last days of April, 1942.
A lot of this was also just looking for middle ground though. Not something as good as the mustang, just something closer to what the P-47C, P-40, or even P-39 could manage in 1941/42. (except not the P-47 since it wasn't combat ready yet, let alone in sufficient numbers) Or for that matter, similar to the P-38 or P-51/Mustang I's combat radius without drop tanks.
The RAF didn't need a 'long' range fighter in the USAAF sense for this scenario ... just a normal/medium range one rather than the short range aircraft they actually had in force.
Basically the practical radius of a standard typhoon was closer to 250 miles if you count the combat allowance and provide a decent reserve.
Yes, which is why I brought it up with the specific context of expanding internal fuel capacity as well.
And given the timing of the Mustang and Spitfire IX, a medium/long range Tempest might still have been useful. (Spitfire IX with expanded fuel capacity would probably the main target though)